Method for connecting superimposed layers of sheet material and apparatus for carrying out the method

ABSTRACT

Stacks of superimposed sheet material are moved at identical spacing sequentially underneath the peripher of a rotating drive. A thread, from which thread staples for connecting the sheet material are to be made, is withdrawn from a bobbin and supplied to the disc where it is engaged and circumferentially entrained. The thread is severed into lengths from each of which one or more thread staples can be made; in the latter case, the length is further subdivided into sections which each correspond to one thread staple length. The thus-obtained thread staples are stitched through the sheet material of a proximal stack. When the thread staples are not to be made sequentially but at intervals, and in the intervals between successive stacks, the supply of thread to the disc is interrupted.

Biittcher METHOD FOR CONNECTING SUPERIMPOSED LAYERS 0F SHEET MATERIAL AND APPARATUS FOR CARRYING OUT THE METHOD Inventor: Winfried Biittcher, Leipzig,

Germany [73 Assignee: Veb Polygraph Leipzig, Leipzig,

Germany Filed: Dec. 30, 1971 Appl. No.: 214,232

US. Cl 112/21, 112/262, 227/81 Int. Cl B42b-l/02 Field of Search 112/21, 48, 262;

References Cited UNITED STATES PATENTS 9/1965 Randall 227/5 FOREIGN PATENTS OR APPLICATIONS 3/1966 Switzerland 471972 Alsop I: ..227/s1g [451 Oct. 9, 1973 Primary Examiner-Werner H. Schroeder Att0mey-Michael S. Striker ABSTRACT Stacks of superimposed sheet material are moved at identical spacing sequentially underneath the peripher of a rotating drive. A thread, from which thread staples for connecting the sheet material are to be made, is withdrawn from a bobbin and supplied to the disc where it is engaged and circumferentially entrained. The thread is severed into lengths from each of which one or more thread staples can be made; in the latter case, the length is further subdivided into sections which each correspond to one thread staple length. The thus-obtained thread staples are stitched through the sheet material of a proximal stack. When the thread staples are not to be made sequentially but at intervals, and in the intervals between successive stacks, the supply of thread to the disc is interrupted.

13 Claims, 5 Drawing Figures PATENTEDUCT 9mm sum 2 [IF 3 METHOD FOR CONNECTING SUPERIMPOSED LAYERS OF SHEET MATERIAL AND APPARATUS FOR CARRYING OUT THE METHOD BACKGROUND OF THE INVENTION The present invention relates generally to the connecting of sheet material layers, and more particularly to a method of effecting such connection and to an apparatus for carrying out the method.

It is already known to connect superimposed layers of-sheet material, usually paper, for instance to form brochures, pamphlets or the like. The connection usually takes place in the fold where the superimposed layers have been already folded, or along a line along which they will be folded after the connection is established. Basically, two types of penetrating connections are known, namely wire staples which are pushed through the superimposed layers or threads which form stitches connecting them. It is also known to employ thread essentially in the same manner as a staple, namely to utilize individual lengths of thread the opposite ends of which are pushed through the superimposed layers from one to the other major side thereof, where the opposite free ends are then connected with the layers by heat-sealing or in other manner. A device for carrying this into effect is known from my copending application Ser. No. 213,255,.filed on Dec. 29, 1971 under the title OPERATOR FOR STITCHING SHEET MATERIALS. Reference may also be had for further information to U.S. Pat. No. 2,541,367, British Pat. No. 638,809, and GDR (East German) Pat. No. 75,297.

Generally speaking, such devices utilize a plurality of thread inserting and fastening devices which are arranged in a direction transversely to the advancement of the superimposed stacks of sheet material and to the folding line, and which can be adjusted with reference to one another. These devices are either of the type utilizing a so-called thread disc, a thread star or a drum, which are rotated in stepwise manner. It is their purpose to withdraw the thread from a supply bobbin or the like, and to supply it to the device which severs the thread into lengths or increments of requisite size, pushes the ends through the stack of sheet material and connects the free ends to the sheet material. One such device, in which the thread is constantly held in the thread disc and taken along with each stepwise turn thereof, is for instance disclosed in GDR Pat; No. 33,685.

The difficulty with the prior art devices which feed sheets transversely to the folding line, is that for each stitch which is to be formed, a separate sealing or connecting device is necessary, which makes it possible to vary the number and spacing of the stitches per unit of length only in narrow limits. In other words, where the thread is employed in the aforementioned manneranalogous to staples, rather than being'sewn through the superimposed sheet material, the formation of a row of stitches requires the formation or existance of a row of devices each of which forms one of the stitches.

Also, with the prior art the superimposed sheet materials must be at rest, that is they must not move with respect to the device securing the free ends of the pushed-through thread lengths to the sheet materials, at least at such times as the thread is being pushed through and the free ends are secured to the sheet materials. This means that either the sheet materials must be stationary during this'time period or that the device for pushing the thread through and connecting the free ends with the sheet materials must move with the sheet materials in the same direction and at the same speed. This, in turn, either requires a slow rate of production or, where synchronism of movement must be obtained, a high technical expenditure.

In addition, it has been found that the known devices of this type can be only of limited use in conjunction with apparatus having a high output, for instance folding apparatus in which the superimposed sheet materi als are folded. The only way these devices can be used with apparatus of this type is if the output from the apparatus is distributed to a relatively large number of different devices, which of course requires distributing arrangements which in turn still further increase the technical and economic expenditures involved.

In other prior-art devices, the disc or analogous eletion of the same. The thread, engaged by the requisite clamping means, surrounds the disc and is being pulled off the supply bobbin thereby; the loop surrounding the disc is cut into sections each eorrespondingin length to that required for forming a thread staple. The free ends of each section are then stitched through a sheetmaterial stack from one to the other major side thereof, deflected against the stack and sealed thereto. How.- ever, such drive can form thread staples only cntinu ously; this formation cannot be interrupted even if no stack of sheet material is located beneath the disc, nor can the intervals between the thread staples be changed. This results in unnecessary thread loss, and in the formation of thread sections whichcannot be used as staples and which, due to-their uncontrolled pres SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the aforementioned disadvantages.

More particularly, it is an object of the present invention to provide .a method which overcomes the disadvantages outlined above, and an apparatus for carrying out the method.

A concomitant object of the invention is to make it possible to employ devices of the general type under discussion even in conjunction with a high-output apparatus and requiring only a single stitchingand connecting device.

Still another object of the invention is to provide for the possibility of forming the stitches at any desired speed of movement of the superimposed sheet materials and in such a manner that the number and spacing of the stitches per stack of sheet materials can be varied within wide limits. I

In pursuance of the above objects, and of others which will become apparent hereafter, one feature of the invention resides in a method of connecting superimposed layers of sheet material which, briefly stated comprises moving a stack of superimposed layers of sheet material past a connecting station, withdrawing thread from a source and supplying it to the connecting station. The thread is severed at the connecting station into lengths each requisite for forming at least one thread staple and such lengths are then stitched through the stack to form thread staples connecting the sheet material of the stack. At such times as no thread staples are being formed, withdrawal of thread and supplying of the same to the station is terminated.

It is advantageous in accordance with the present invention that the thread is withdrawn incrementally from the supply, before it reaches the connecting station (i.e., the disc), formed into a loop which is then clamped at such a location that the circumferential length of the loop corresponds to the desired requisite length of thread, and that the thus-determined or fixed thread length is then received by the disc during rotation thereof with the loop being dissolved during such rotation.

The apparatus according to the present invention utilizes a thread control means located between the thread supply, that is the bobbin or the like, and the disc receiving the thread. The arrangement may be such that the thread control means utilizes one or two thread clamps, if desired a thread withdrawing arrangement which incrementally withdraws the thread from the supply, and a severing arrangement proximal to the rotary disc.

The thread control means may also utilize a feeding arrangement, for instance in form of an additional disc which is rotatable and carries an additional severing device, with the additional disc having a circumference the distance of which is larger than the length of the required thread increment and which is so mounted for rotation that the circumferential speed of the rotary disc is larger than that of the additional disc.

However, a rockable element can also be utilized in the thread control means and be provided in connection with the additional severing device.

Furthermore, the thread control means may also utilize simply a laterally displaceable thread guide and the additional thread severing device.

It is advantageous, but not necessary, to provide sensing elements of known construction, for instance photo-electric cells, which sense the approach of sheet materials towards the disc and supply a signal to the thread control means indicating the arrival of a new stack of superimposed sheet materials.

Thus, the present invention influences the supply of thread upstream of the rotary disc which effects pushing of the ends of a severed thread length through the material and securing of the free ends of the severed section to the material. This means that the number of such stitches" and the spacing between successive stitches can be varied at will between a virtually continuous succession of stitches and a spacing of stitches thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

from one another. Also, the sequence in which the stacks of sheet materials are supplied, can be varied by optical control of the arrangement. By the low-inertia influencing of the thread guidance and supply, I make it possible to have the rotary disc rotate continuously instead of intermittently, so that this approach to connecting superimposed layers of sheet material can be utilized without additional equipment even in conjunction with high speed machines, that is machines which have a high output of sheet material or sheet material stacks.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic illustration showing a first embodiment of the invention;

FIG'. la is a diagrammatic illustration showing the stitching pattern obtained with the embodiment of FIG.

FIG. 2 is a view similar to FIG. 1, but showing a second embodiment of the invention; and

FIG. 2a is a diagrammatic illustration showing the stitching pattern obtained with the embodiment of FIG.

FIG. 3 is a view similar to FIG. 1, but showing a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 stacks 10 of superimposed sheet material are fed by a non-illustrated feed mechanism in the di-, rection of the arrow and at a feeding speed VB. The spacing between the leading edges of consecutive stacks 10 is always maintained constant, irrespective of the length of the respective stacks.

The stacks move serially beneath an electrically grounded rotary disc 8 which contacts the stacks l0 and is driven in rotation at a circumferential speed VF which corresponds to the feeding speed VB. Also, the circumferential length of the disc corresponds to the aforementioned constant spacing between the leading edges of the respective consecutive stacks.

In this embodiment, as in those of FIGS. 2 and 3, the rotary discs are each provided with eight circumferentially spaced pairs of gripping means, for example sets of clamping springs 7 which are equi-distantly spaced about the circumference of the disc 8. There are also provided eight pairs of stitching or connecting needles 33 which are usually retracted into the interior of disc 8 by non-illustrated springs, and which can be pushed outwardly beyond the disc periphery by a fixed cam 34 located within the disc. Further details of the construction and operation of the components thus far described may be ascertained from the aforementioned GDR Pat. No. 75,297.

Located adjacent the disc 8 is a rotating cutting wheel carrying a pair of cutting blades or edges I3 which rotate at the same circumferential speed as the disc 8. They enter into the slots defined between the springs of each pair of springs7 and cut thread which is clamped and held between these springs.

A-bobbin 1 constitutes a source of thread 14 which is passed through a first brake or stopping device 3, around and beneath a lever 4 so as to form a thread loop 15, through a second brake or stopping device 5,

and then via a thread guide 6 to respective pairs of clamping springs 7 by which it is clampingly engaged. The devices 3 and 5 are connected for cooperation by a double-armed lever 24 which is rockably mounted at its middle on a support 25. A spring 26 permanently tends to draw the (in the drawing) left arm of lever 24 towards the support, thereby tending to keep device 5 in inoperative or open condition and device 3 in operative or closed condition. When, during operation of the device, the thread 14 is pulled by the rotating disc 8,

5. tension of the thread on lever 4 rather the same and the size of the loop 15 decreases.

As already indicated, the stacks 10 are continuously moved from left to right in FIG. 1. The stack to the right side of disc 8 has already been processed, i.e., provided with a desired number of thread staples; the stack 10 underneath disc 8 has just had its first thread staple applied.

It will be seen that at this time a length 11 of thread 14 is supported on the periphery of disc 8, being clampingly held by two circumferentially successive pairs of clamping springs. A further thread length 11, which has just been severed from thread 14 by device 12, is held by the next pairs of springs 7. Additional springs 7 hold the thread 14 which has been pulled out of the diminishing loop 15. The lengths 11 are sequentially stitched through the stack 10 by the needles 33.

A sensing or detecting device is provided for detecting the approach of the stacks 10 to the disc 8. Such a device could be photoelectric in nature, a blowing nozzle or a suction nozzle, or as illustrated it can be an electric switch 16 arranged in the path of increment of the stacks l0.Advantageously, its'position should be shiftable to some extent longitudinally of this path.

After the stack under the disc 8 has the third successive staple stitched into it, its trailing end passes the switch 16 which then closes and energizes an electromagnet 27 which is mounted on support 25 and, when energized, acts to exert upward pull on the right arm of lever 24. The energy for this operation may be supplied by a DC source 28. As electromagnet 27 responds to energizatiomthe device 3 moves to open position while simultaneously the device 5 moves to closed position; this results in braking of further advancement of thread 14. The springs 7 engaging the thread 14 cannot overcome the action of device 5 and merely slip on the thread 14 as the disc8 continues to rotate. In response to such continued rotation, only the last two lengths 11 severed by device 12 can still be stitched into the stack after this, there are no further lengths 11 to be stitched.

Movement of the lever 24 also closes an electric switch 29 which energizes an electromagnet 30. In turn, theelectromagnet 30 lowers lever 4 and thereby pulls a further loop 15 of thread 14 off the bobbin 1; no thread can'be drawn backwardly off the disc 8 because of the clamping action of device 5.

During continued movement of the stacks 10, the one which has just been completely stitched moves past the disc 8 to the right, and the next one approaches. As soon as the leading edge of this next stack causes the switch 16 to open, magnet 27 becomes de-energized. Spring 26 now pulls the lefthand arm of lever 24 up again, opening device 5 and closing device 3. The thread 14 intermediate device 3 and disc 8 having thus 35a engages beneath the right-hand end of lever 24. This results in opening of both of the devices 3 and 5, so that thread 14 can feed continuously and the production of staples is uninterrupted.

There is, however, an additional switch 32 provided, and also the diagrammatically shown contact elements 31 which can be clamped to the reverse side of the'disc 8. Utilizing these components, electromagnetic 27 can be'operated independently of switch 16. If contact elements 31 and 31b are arranged as shown, the device will form thread staples in the manner shown in FIG.

. 1a, because element 31a prevents, by energizing elecbeen released, slippage between it and the springs 7 closes, and the thread is again withdrawn from the new loop 15 and supplied to the cutting device 12.

Of course, in the interval between stacks and also if, for example, one or more stack should be missing from the normally continuous feedno thread staples are being formed, because the switch 16 and device 5 remain closed at such times.

With this embodiment, stapling and stitching can be carried out continuously as in the prior art. For this purpose, the DC. source 28 is switched off via switch 36, and a holding device 35 is turned so that its hook tromagnet 27, feeding of the thread required for forming the second staple which would otherwise be in-' serted at 3lal', whereas element 311) prevents feeding of thread for forming of the fourth staple which would otherwise be inserted at 31b. Inasmuch as the needles 33 operate continuously, however, they will merely pierce two holes in the stack 10'every time there is no thread for making a staple present when the needles are operated.

In the embodiment of FIG. 2, the elements 8, 12, 13, 33 and 34 (the latter two are not shown) are the same as in FIG. 1. Disc 8 has, however, additionally mounted on it two grippers 21 which are controlled by a fixed cam 23 and are pivotally mounted as shown.

A thread feeding disc 20 is located adjacent to, but out of contact with the disc 8; it carries four pairs of equi-angularly spaced clamping springs 19. The circumferential length of disc 20 is half that of disc 8, and the same relationship prevails in their circumferential speeds. Thread 14 is pulled off the bobbin 1 by disc 20 and its leading end supplied to the respectively uppermost gripper 21 in synchronism with the arrival of the same in uppermost position.

This embodiment can produce thread staples as shown in FIG. 2a, i.e., the stack 10 is provided with two consecutive thread staples, a space corresponding to the length of two thread lengths 11 remains free, and two further consecutive thread staples are formed.

Incidentally, in the subsequently following interval between the first finished stack and the next one, which interval may be the same as or smaller than the space corresponding to two thread lengths 11, the formation of staples must be prevented. The FIG. 2 embodiment makes this possible. Disc 8 and stacks 10 move synchronously and in the illustrated position a first staple in the stack 10 has just been inserted by the nonillustrated needles 33. At this time, a further thread length 11 is held between the next following springs 7.

A fixed contact 31 on disc 8, and a switch 32, will now energize very briefly the electromagnet 27, causing the cutting device 18 to be pulled against feed disc 20, thus severing between a pair of clamping springs 19 the thread held by them. There is now produced a thread length 17 sufficient to form two staples, and

whose leading end will be gripped by the upper gripper device 21 which pivots in such a manner that it nips the leading end against the disc 8 periphery. Because the circumferential speed of disc 8 is twice that of disc 20, the length 17 will be pulled loose from springs 17 and engaged by springs 7 of disc 8. In the meanwhile, a second staple has been formed in the stack 10.

However, because only one length 17 of twice the length of a staple is being pulled along behind the one gripper 21, no thread is engaged by the clamping springs intermediate the two grippers 21 and the next following two stitching operations of the needles will therefore be carried out without thread, and, hence, without forming stitches.

When the gripper 21 trailing the length 17 has passed the stack, two more staples will be produced, and during the time interval between the now-completed stack and the next one, there is again no thread available for staple formation. The rotating device 12 subdivides the length 17 into two lengths 1 1 each of which is sufficient to form one staple.

The embodiment of FIG. 3, finally, has no thread feeding disc. The cutting device 18 is here controlled in the same manner as discussed relative to FIG. 2, and

severs a thread piece whose length is such that all staples can be made from it which are needed for an individual stack 10. Staples are produced and inserted one after another, without any spacing. Inasmuch as only one gripper device 21 is provided in this embodiment, only one staple-making interruption is possible during each revolution of disc 8, and this comes during the interval between two successive stacks 10.

The device 18 is operated as before, by an electromagnet 27 which is energized by a contact element 31 cooperating with switch 32. When the thread is cut into lengths, the free end of each length slips over the circumference of disc 8 until engaged and held by gripper device 21, whereupon it is pulled into engagement with gripper 7. The device 13 then severs each length into lengths 11 corresponding to one staple.

While the invention has been illustrated and described as embodied in an apparatus for connecting superimposed sheet-material layers, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 7

Without further analysis the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of connecting superimposed sheet material by thread staples, comprising the steps of continuously moving stacks of superimposed sheet material past a connecting station; withdrawing thread from a source and supplying it to said connecting station; severing the thread at said connecting station into lengths each requisite for forming at least one thread staple; stitching said lengths through said stacks so as to form thread staples connecting the sheet material thereof; and interrupting supply of thread to said connecting station during continued movement of said stacks of superimposed sheet material at such times at which no thread staples are to be stitched through said stacks which are continuously being moved past said connecting station.

2. In an apparatus for connecting stacked superimposed sheet material by thread staples, in combination, feeding means for continuously feeding stacks of said superimposed sheet material; supply means for supply ing a thread; rotary disc means, continuously rotating with a peripheral speed corresponding to the feeding speed of said stacks of superimposed sheet material, said rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through respective stacks of said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interruping the supply of thread to said severing means at such times as no thread staples are to be stitched through said stacks which are continuously being moved past said stitching means.

3. A method of connecting superimposed sheet material by thread staples, comprising the steps of moving a stack of superimposed sheet material past a connecting station; withdrawing thread from a source and supplying it to said connecting station; severing the thread at said connecting station into lengths each corresponding to at least two thread staples; subdividing each length into sections which are respectively requisite for forming a single thread staple; stitching said lengths through said stack so as to form thread staples connecting the sheet material thereof; and interrupting withdrawal of thread from said source at such times at which no thread staples are to be formed.

4. A method of connecting superimposed sheet material by thread staples, comprising the steps of moving a stack of superimposed sheet material past a connecting station; withdrawing thread from a source; and forming it upstream of said connecting station into loops each having a length requisite for forming at least one thread staple; clamping each loop at the upstream end thereof; supplying the thread constituting the respective loop to said connecting station while terminating the step of clamping; severing the thread at said connecting station into lengths each requisite for forming at least one thread staple; stitching said lengths through said stack so as to form thread staples connecting the sheet material thereof; and interrupting withdrawal of the thread from said source at such times at which no thread staples are to be formed.

5. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means being interposed between said supply means and said disc means.

6. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supplymeans for supplying a thread; rotary disc means 1 having a periphery for receiving said thread; stitching cated intermediate said thread clamp and said disc means in the region of the latter.

7. In an apparatus as defined in claim 6, said control means further comprising thread withdrawing means upstream of said severing means, for incrementally withdrawing thread from said supply means.

8. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for'supplying a thread; rotary disc means having a periphery receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising feed means for receiving increments of thread from said supply means and feeding them to said discmeans; and additional severing means cooperating with said feed means for severing said increments from said thread prior to supplying of such increments to said disc means.

9. In an apparatus as defined in claim 8, wherein said additional severing means is carried by said feed means.

10. In an'apparatus as defined in claim 8, said feed means comprising a rotatable disc member having a peripheral length greater than said requisite length, and rotating at a peripheral speed smaller than that of said rotary disc means.

11. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be.

formed by said stitching means, said control means comprising rockable gripper means, and additional severing means.

12. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengthsfor conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising thread guide means upstream of said disc means, and additional severing means for severing said thread intermediate said thread guide means and said disc means.

13. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising at least one thread controlling device; and at least one sensing device positioned for sensing the approach of respective stacks of sheet material to said disc means, said sensing device being operatively associated with said thread controlling device for effecting operation of the same in a sense permitting supply of thread towards said disc means in response to the sensing of such approach. 

1. A method of connecting superimposed sheet material by thread staples, comprising the steps of continuously moving stacks of superimposed sheet material past a connecting station; withdrawing thread from a source and supplying it to said connecting station; severing the thread at said connecting station into lengths each requisite for forming at least one thread staple; stitching said lengths through said stacks so as to form thread staples connecting the sheet material thereof; and interrupting supply of thread to said connecting station during continued movement of said stacks of superimposed sheet material at such times at which no thread staples are to be stitched through said stacks which are continuously being moved past said connecting station.
 2. In an apparatus for connecting stacked superimposed sheet material by thread staples, in combination, feeding means for continuously feeding stacks of said superimposed sheet material; supply means for supplying a thread; rotary disc means, continuously rotating with a peripheral speed corresponding to the feeding speed of said stacks of superimposed sheet material, said rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through respective stacks of said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be stitched through said stacks which are continuously being moved past said stitching means.
 3. A method of connecting superimposed sheet material by thread staples, comprising the steps of moving a stack of superimposed sheet material past a connecting station; withdrawing thread from a source and supplying it to said connecting station; severing the thread at said connecting station into lengths each corresponding to at least two thread staples; subdividing each length into sections which are respectively requisite for forming a single thread staple; stitching said lengths through said stack so as to form thread staples connecting the sheet material thereof; and interrupting withdrawal of thread from said source at such times at which no thread staples are to be formed.
 4. A method of connecting superimposed sheet material by thread staples, comprising the steps of moving a stack of superimposed sheet material past a connecting station; withdrawing thread from a source; and forming it upstream of said connecting station into loops each having a length requisite for forming at least one thread staple; clamping each loop at the upstream end thereof; supplying the thread constituting the respective loop to said connecting station while terminating the step of clamping; severing the thread at said connecting station into lengths each requisite for forming at least one thread staple; stitching said lengths through said stack so as to form thread staples connecting the sheet material thereof; and interrupting withdrawal of the thread from said source at such times at which no thread staples are to be formed.
 5. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means being interposed between said supply means and said disc means.
 6. In an apparatus for connecting staCked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising at least one thread clamp for clampingly engaging said thread, and said severing means being located intermediate said thread clamp and said disc means in the region of the latter.
 7. In an apparatus as defined in claim 6, said control means further comprising thread withdrawing means upstream of said severing means, for incrementally withdrawing thread from said supply means.
 8. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising feed means for receiving increments of thread from said supply means and feeding them to said disc means; and additional severing means cooperating with said feed means for severing said increments from said thread prior to supplying of such increments to said disc means.
 9. In an apparatus as defined in claim 8, wherein said additional severing means is carried by said feed means.
 10. In an apparatus as defined in claim 8, said feed means comprising a rotatable disc member having a peripheral length greater than said requisite length, and rotating at a peripheral speed smaller than that of said rotary disc means.
 11. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising rockable gripper means, and additional severing means.
 12. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control means for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising thread guide means upstream of said disc means, and additional severing means for severing said thread intermediate said thread guide means and said disc means.
 13. In an apparatus for connecting stacked superimposed sheet material by thread staples, comprising supply means for supplying a thread; rotary disc means having a periphery for receiving said thread; stitching means for stitching lengths of said thread through said superimposed sheet material; severing means for severing from said thread requisite lengths for conversion by said stitching means into thread staples; and control mEans for interrupting the supply of thread to said severing means at such times as no thread staples are to be formed by said stitching means, said control means comprising at least one thread controlling device; and at least one sensing device positioned for sensing the approach of respective stacks of sheet material to said disc means, said sensing device being operatively associated with said thread controlling device for effecting operation of the same in a sense permitting supply of thread towards said disc means in response to the sensing of such approach. 